import java.util.*;

public class Main {
	public static void main (String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] dp = new int[n + 3];
		for (int i = 3; i < n + 3; i++) {
		    int x = sc.nextInt();
		    dp[i] = Math.max(dp[i - 2], dp[i - 3]) + x;
		}
		System.out.println(Math.max(dp[n + 2], dp[n + 1]));
	}
}